VIRAL DYNAMICS - A MODEL OF THE EFFECTS OF SIZE, SHAPE, MOTION AND ABUNDANCE OF SINGLE-CELLED PLANKTONIC ORGANISMS AND OTHER PARTICLES

The transport of aquatic viruses to particles can be described in terms of diffusive transport from solution. Such transport is influenced by motion of the water relative to the particle. Because transport rate is determined purely by physical factors it is independent of whether the particle is a host or non-host organism. The low viral diffusivity relative to that for dissolved nutrients makes transport enhancement from organism swimming more important for viruses. The virus contact rate with bacteria is relatively unaffected by such motions because of small bacterial sizes. Transport rates for phytoplankton and protozoa can increase over an order of magnitude when swimming motions are considered. Although larger organisms have much higher transport rates per individual, their far lower concentrations in sea water should make small organisms the preferred targets for viruses. Rates of host-virus interactions in culture are closely related to predictions from transport theory. There is a fairly close relationship between bacterial populations and virus disappearance rates in the marine environment, suggesting that non-host organisms are a major cause of viral mortality at the higher ionic strengths typical of sea water. Other factors, such as UV radiation, must also be included when estimating viral mortality in seawater.